Countertop oven



FIG. 1 is top, front and left-side perspective view of a countertop oven showing our new design;

FIG. 2 is a front elevation view thereof;

FIG. 3 is a right side elevation view thereof;

FIG. 4 is a left side elevation view thereof;

FIG. 5 is a top plan view thereof; and,

FIG. 6 is a bottom plan view thereof.

The broken lines in the drawings are for illustrative purposes only and form no part of the claimed design. 

The ornamental design for a countertop oven, as shown and described. 